
Hi Nicola,
First of all, don't let him eat (human) chocolate! It's poisonous for dogs.
It's hard to advise on what's best to do without seeing the dog, but what I would try is to start to convince him that you aren't the meany who takes away all the nice things - you're the goodie who gives them to him! To do this I would start at his mealtimes, by measuring out his ration, holding his bowl empty, and put a small handful of his food into it, and let him eat that. Then add another small handful, and another, until his ration is finished. After a week or two of this, especially if he is fed more than once a day, he will be seeing you as less of a threat.
Regarding stealing from the worktop - I've had to learn not to leave things out! (Not meaning to be flippant!)
When you want to take something from him, offer him a swop. Sound happy and cheerful and confident, and say "Look what I've got! Come see? D'you want it?" Overact, ham it up something rotten - dogs like this and it relaxes them. The more anxious you get about it, the more important he'll think the item is and be even more possessive of it.
Good luck. :)